The overall goal of this Project is to determine the relative importance of the de novo and salvage pathways for the synthesis of pyrimidine nucleotides in normal and malignant tissues in vivo. i.e., in the intact animal. This can be accomplished because of two recent advances in our Laboratory: (a) development of GC/MS methodology and a novel method of data analysis to quantitate pyrimidine de novo pathway activity and (b) discovery of an inhibitor of uridine kinase that is an effective inhibitor of pyrimidine salvage in vivo. These two tools will be used to assess the de novo and salvage pathways as targets for future antitumor drug development, as well as the therapeutic value of concurrent inhibition of both pathways. Early comparative data indicate that uridine salvage makes a substantial contribution to lhe pyrimidine nucleotide pools of mouse liver, intestine, and kidney in the intact animal. Activation of uridine salvage is an early event in the mitogenic response, occurring within minutes of serum stimulation of quiescent fibroblasts. Data from our early experiments into the mechanism responsible for this activation indicate that it is linked to the synthesis of components of the extracellular matrix (specifically, hyaluronate). Current studies will evaluate the effects of inhibitors of hyaluronate synthesis on the activation of uridine salvage and on the invasive and metastatic properties of cancer cells.